Adhesive compositions, such as pressure-sensitive adhesive (PSA) compositions, commonly contain an adhesive polymer together with a tackifier or plasticizer. The adhesive polymer provides cohesion and the tackifier or plasticizer increases tack.
Adhesives are useful in a wide range of applications and include PSAs which are used in labels, masking tapes and protective coverings. Further, pressure sensitive adhesive compositions which are water-dispersible are used for fastening cloth on mammalian body coverings and in papermaking and printing operations. In papermaking they may be used, for example, to splice the end of one roll of paper to the beginning of another roll.
In papermaking, in particular, it is desirable that the adhesives used are repulpable. That is, they can be left with the paper to be repulped without interfering with subsequent papermaking processes and are free of components which would blemish the final paper product. To be repulpable, such adhesives should be water soluble or water dispersible.
The current trend in papermaking is away from acid processing conditions toward alkaline processing conditions and toward an increased use of calcium carbonate filler. Conventional repulpable adhesives are usually unsuitable for such alkaline conditions. Further, those adhesives which might be suitable, tend to react with the calcium ions of a calcium carbonate filler to form agglomerates which decrease the solubility of the adhesive copolymers.
Adhesives used for splicing in the paper industry may be subjected to elevated temperatures under high shear forces, for example in supercalender applications. Any slippage, even fractions of a millimeter, may lead to blocking and subsequent web breakage. A high cohesive strength is desirable to withstand high pressure and heat, to resist lateral adhesive flow or "oozing" (which would result in slippage) and to resist adhesive loss by penetration into the paper or "bleeding". Further, an adhesive for use in papermaking is preferably repulpable under a variety of pH conditions (both alkaline and acidic).